Linear motion guide units have been extensively applied in recent years between two parts which slide relative to each other for linear reciprocating mechanism used in increased industrial fields including semiconductor fabricating equipment, machine tools, industrial robots, and so on. Recently advanced machines and instruments are increasingly required energy saving, simple construction and less production cost, and further in need of keeping running cost and maintenance cost of equipment reasonably less than ever. Correspondingly, the linear motion guide units incorporated in the advanced machinery are also challenged to make their construction compact and simplified, keeping down the production cost while ensuring the current performances, along with realizing virtual maintenance-free operating condition for lubrication.
In the commonly assigned Japanese Laid-Open Patent Application No. 2003-90 338 referred later as patent literature 1, there is disclosed a linear motion guide unit in which tubular connectors are installed to communicate turnaround passages with their associated return passage. The prior linear motion guide unit constructed as recited earlier is envisaged making sure of smooth recirculation of the ball rolling elements as well as long-lasting continuous application of lubricant around the rolling elements so as to realize the virtual maintenance-free operating condition for lubrication. With the prior linear motion guide unit, the maintenance-free operation for lubrication has been made possible by the tubular connectors which join the turnaround passages to the return passages of sintered resinous material of cellular texture to complete the smooth circulating circuit. Moreover, the slider is composed of a carriage having a through-bore, a tubular member inserted into the through-bore to define the return passage, the tubular member in lengthwise dimension being short of the carriage to lay the through-bore bare at lengthwise opposite ends after the tubular member has been inserted inside the through-bore, a spacer having a spacer part to provide an inside circular half of the turnaround passage and an inside circular half of the tubular connector, which comes into mating with the inside circular half of the turnaround passage to form the end of the return passage, and an end cap to provide an outside circular half of the turnaround passage and an outside circular half of the tubular connector, which comes into mating with the outside circular half of the turnaround passage to form the end of the return passage.
Another linear guide device is disclosed in Japanese Laid-Open Utility Model Application No. S61-85 716, in which a carriage of a slider has lengthwise grooves on widthwise opposite sides thereof, the grooves being closed with closure plates to provide passage to allow balls returning through there. With the prior linear guide device, the closure plates to provide the return passages have widthwise dimensions enough to close the grooves cut on the sides of the carriage across the overall length of the carriage and lengthwise dimensions more than the overall length of the carriage. The closure plates are held at their ends with end caps.
With the linear motion guide unit disclosed in the patent literature 1, as shown in FIGS. 1 to 5 in the patent gazette of Japanese Laid-Open Patent Application No. 2003-90 338, the through-bore is formed in the carriage of the slider and then the tubular member is inserted in the through-bore to provide the return passage. This drilling or boring operation to make the through-hole is difficult to make with high precision and has a high working cost. Thus, this prior art poses a serious challenge in compact, simple construction and reduced production cost.
The linear guide device disclosed in Japanese Laid-Open Utility Model Application No. S61-85 716 has no concept or motivation of developing a maintenance-free operation in which the lubricant is applied around the rolling elements at the return passages. In the prior guide device, moreover, a further challenge still remains about how many components or parts are mutually arranged with accuracy to make certain of smooth circulation of the rolling elements.
The miniature linear motion guide unit of the present invention, while being a derivation from the commonly-assigned Japanese Laid-Open Patent Application No. 2012-47 288, is a further development of the same technical concept in the linear motion guide unit disclosed in the commonly-assigned senior Japanese patent application No. 2013-15189. The miniature linear motion guide unit of the present invention is focused on the subject matter about what construction makes cost reductions possible in compliance with recent need for cost savings in production. With the miniature linear motion guide unit of the present invention, especially, a tubular member to form a return passage or a covering to embrace the tubular member is made integrally with an end cap or, as an alternative, separately from the end cap so as to facilitate and simplify assembly of the components for the sake of cost savings while carrying out maintenance-free for lubrication to get the ball rolling elements smoothly circulating.